This invention relates to a coating solution for forming a charge generation layer and an electrophotographic photoreceptor using the same.
In the prior art, in an electrophotographic photoreceptor in which a photoconductive substance is used as a photosensitive material, inorganic photoconductive substances such as selenium, zinc oxide, titanium oxide and cadmium oxide have been mainly used. However, many of these substances have strong toxicity so that they have also problems in disposal methods.
On the other hand, in general, when organic photoconductive compounds are used, toxicity is weaker and there are advantages in the points of transparency, flexibility, light-weight property, surface smoothness and price as compared with the case of using inorganic photoconductive substances. Therefore, electrophotographic photoreceptors using organic photoconductive compounds have been studied widely. When these photoreceptors are applied to an electrophotographic device according to the Carlson method, an image can be obtained by forming an electrostatic image on the surface of the photoreceptor, developing the photoreceptor by a developer, the so-called toner, charged to the same charge (+ or -) as or a different charge from that of the electrostatic image, and then transferring and fixing a toner image onto a different substrate such as paper.
In recent years, there have been reported many photoreceptors using an organic photoconductive compound and having sensitivity to around 800 nm which is the wavelength of a diode laser region. However, in many of these, a phthalocyanine pigment is used as a charge generation substance, and a photosensitive layer is formed by using a coating solution obtained by dispersing the pigment in a binder resin.
In phthalocyanines which are pigments, not only absorption spectrum and photoconductivity vary depending on central metals, but also these physical properties vary depending on crystal forms. There have been reported several examples of phthalocyanines in which the same central metal is used, but a specific crystal form is selected for an electrophotographic photoreceptor.
For example, there has been reported that various crystal forms exist in titanylphthalocyanines, and charging characteristics, dark decay and sensitivity vary greatly depending on the difference of their crystal forms.
In Japanese Provisional Patent Publication No. 49544/1984, it has been described that a crystal form of titanylphthalocyanine giving strong diffraction peaks at 9.2.degree., 13.1.degree., 20.7.degree., 26.2.degree. and 27.1.degree. of Bragg angles (2.theta..+-.0.2.degree.) is preferred, and an X-ray diffraction spectrum chart is shown.
Also, in Japanese Provisional Patent Publication No. 166959/1984, there has been shown a charge generation layer obtained by allowing a vapor deposited film of titanylphthalocyanine to stand in tetrahydrofuran-saturated vapor for 1 to 24 hours to change a crystal form. It has been shown that the X-ray diffraction spectrum shows a smaller number of wide peaks and gives strong diffraction peaks at 7.5.degree., 12.6.degree., 13.0.degree., 25.4.degree., 26.2.degree. and 28.6.degree. of Bragg angles (2.theta.).
Further, in Japanese Provisional Patent Publication No. 17066/1989, there has been described that a crystal form of titanylphthalocyanine having main peaks at least at 9.5.degree., 9.7.degree., 11.7.degree., 15.0.degree., 23.5.degree., 24.1.degree. and 27.3.degree. of Bragg angles (2.theta..+-.0.2.degree.) is preferred.
In Japanese Provisional Patent Publications No. 131243/1990 and No. 214867/1990, there has been described that a crystal form of titanylphthalocyanine having a main diffraction peak at 27.3.degree. of Bragg angles is preferred.
As described above, titanylphthalocyanine exhibits extremely high sensitivity and excellent characteristics by changing a crystal form. However, in a laser printer for which it is used, higher quality and higher precision have been achieved, and an electrophotographic photoreceptor having further high sensitivity characteristic has been demanded.
As a binder resin, there have been used a polyester resin, a polyvinyl chloride resin, a silicone resin, a polystyrene resin, a polyvinyl butyral resin and a phenoxy resin.
In Japanese Provisional Patent Publication No. 183263/1990, there has been shown titanylphthalocyanine with which a polyester resin as a binder resin and 1,2-dichloroethane as a dispersion solvent are used.
In Japanese Provisional Patent Publication No. 231753/1991, there has been shown X type non-metal phthalocyanine with which a modified polyvinyl chloride resin as a binder resin and tetrahydrofuran as a dispersion solvent are used.
In Japanese Provisional Patent Publication No. 10257/1991, there has been shown titanylphthalocyanine with which a polyhydroxystyrene resin as a binder resin and ethanol as a dispersion solvent are used.
In Japanese Provisional Patent Publication No. 33863/1991, there has been shown titanylphthalocyanine with which an acryl resin as a binder resin and cyclohexanone as a dispersion solvent are used.
In Japanese Provisional Patent Publication No. 33863/1991, there has been shown titanylphthalocyanine with which a phenol resin as a binder resin and methyl isobutyl ketone as a dispersion solvent are used.
In Japanese Provisional Patent Publication No. 81861/1992, there has been shown titanylphthalocyanine with which a polyvinyl butyral resin as a binder resin and 1,2-di-methoxyethane as a dispersion solvent are used.
However, in either case, electrophotographic characteristics such as charging characteristics, dark decay and sensitivity are not necessarily satisfactory, and a halogen type solvent having problems in dispersion stability, coating property, electrophotographic characteristics and environmental sanitation is required to be used as a dispersion solvent.